Known are so called Pod-Drives for boats, which are also referred to as pivoting boat drives or a rudder propeller. Such boat drives, for simultaneously steering and driving a boat, have a transmission unit inside the hull and a steering unit below the hull in the water. At least one propeller is pivotally positioned at the steering unit and is driven by a propeller shaft which is rotatably positioned within the steering housing. The steering unit pivots around its vertical axis to steer the boat, mainly, pivoting in parallel to the vertical axis of the boat. The transmission unit is coupled to a drive motor via a drive shaft. The drive motor is, like the transmission unit, positioned inside of the hull. An angle drive is positioned in the transmission unit to transfer the drive power down to the propeller shaft. In the angle drive, or in an optional gear ratio step, reversal of the rotational speed or torque, respectively, is possible as is reversal of the shaft rotation. The transmission units in the state of the art have just one shaft connection which is connected with the drive shaft or the engine, respectively. If an additional drive motor shall drive the propeller, as it is required for instance in a hybrid drive in which an additional electrical motor needs to be provided as an alternative drive motor, the transmission unit requires hereby a so-called auxiliary drive. The advantage of the electric motor in a hybrid drive is its possible application in areas of operation where noise and/or exhaust gases are to be limited or in lower speed mode operation such as a slow ride or when maneuvering during docking or takeoff.
In the following, an auxiliary drive needs to be understood as a technical device which allows the connection to an additional drive motor and the transfer of the input power to an output or output shaft, respectively. Also, it makes sense in certain cases of application to have a configuration with two different drive motor sizes, whereby the more powerful drive motor operates in a first operating range with a high power demand, for instance at high speeds or tensile loads, and where the lower power drive motor operates at lower load. Through the alternative operation of several engines, each can be operated using its best efficiency.
The DE 69933288 T2 shows a pivoting boat drive which, however, cannot be driven by means of an alternative drive motor. To create an auxiliary drive, a new transmission unit needs to be constructed or the existing transmission unit needs to be redesigned or altered. A hybridization of an existing boat drive in the described art is therefore only possible with significant effort.
The EP 1259423 B1 shows a two-engine boat drive configuration. Hereby, a boat transmission has two input shafts for each drive motor. The input shafts can be coupled selectively with the propeller shaft by means of several clutches, or they can drive the propeller shaft together. Even when the operation of the boat drive requires just one drive motor, both input shafts are present in the transmission, meaning that the transmission construction is more sophisticated than it is required which is noticeable through higher cost or installation effort, respectively, and weight. To the contrary, if the transmission is designed with one drive that is to be driven by just one drive motor, the second, unused input shaft can be omitted during the installation of the transmission. If the boat drive, however, needs to be altered to a two-engine operation, significant modification is hereby required. In addition, the described transmission is not suited for a pivoting boat drive because angular deflection the power shafts, which is required for a rudder propeller, is not provided here.